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Encephalin. Computer molecular graphic of part of a molecule of encephalin, a polypeptide found in the human brain. It has a painkilling effect, and is also thought to affect mood and to stimulate motivation. Encephalin is a small protein molecule made up of five peptides (a pentapeptide). These peptides are in turn made up of amino acids. The atoms (coloured spheres) of the molecule include carbon (yellow) as well as hydrogen, oxygen and nitrogen. Produced naturally in the brain and by nerve endings elsewhere in the body, encephalin's analgesic (painkilling) effects resemble those of the drugs morphine and codeine. A genetic autoradiogram is seen in the background.